Optimizing the operation of an internal combustion engine (or engine) for power, efficiency, and emissions typically involves monitoring or sensing one or multiple parameters that affect combustion and adjusting ignition and fuel scheduling based on the sensor outputs. These parameters can include, for example, any one or more of engine speed, acceleration/deceleration, cylinder head temperature, mass air flow, manifold pressure, crank position, oxygen content in the exhaust and engine load. The temperature of an internal combustion engine can affect engine starting and performance, and so it is desirable to monitor cylinder head temperature and thereby adjust any of a variety of aspects of engine operation that are dependent upon temperature, including ignition timing and air-to-fuel ratios, in order to optimize engine performance. Among other things, engine cylinder head temperature is typically important for determining air-to-fuel ratios. For example, when the cylinder head temperature is less than about 70 degrees Fahrenheit, cold enrichment becomes appropriate.
Carbureted engines include certain features that allow engines to be operated in manners by which various conditions, and particularly varying temperature conditions, are taken into account. However, such designs also can entail certain disadvantages. For example, many carbureted engines include a choke by which the air-to-fuel ratio can be adjusted manually by an operator. Yet such systems are limited because actuation of the choke involves guess work on the part of the operator as to the level of actuation of the choke that is appropriate under any given circumstance, and further because in many such embodiments the choke is controlled at least in part by way of a temperature sensitive spring that can introduce inaccuracy and drift into the system. Also for example, other more complicated engines such as engines that employ electronic fuel injection may include a fully automated system that can employ temperature information measured by way of a thyristor or other sensing element(s) that serves to sense engine (e.g., cylinder head) temperature. Yet the thyristor or other additional sensing element(s) typically is or are additional components that add cost to the system. For these reasons and/or other reasons, it would be advantageous if simplified or improved systems and methods for engine temperature sensing could be developed.